1. Field of the Invention
The present invention relates to a new aniline polymer and to materials for an electrode and a secondary cell comprising the new aniline polymer.
2. Description of the Prior Art
In recent years, transportability of communication and office automation (OA) equipments has been advanced and competition to make them lightweight and small size is becoming fierce. It has also been requested to improve the efficiency of a secondary cell used as a power source in various equipments, or a power source for an electric car and the like.
In response to these demands, secondary cells using new materials for an electrode have been developed. Among them, attention is drawn to materials for electrodes comprising a disulfide compound because of its comparatively high energy density (as disclosed in U.S. Pat. No. 4,833,048, etc.).
In such a disulfide compound to be used as an electrode material, there is a disulfide linkage containing two sulfur elements between groups consisting of two organic substances (R--S--S--R'). The S--S linkage is cleaved by supply of two electrons through electrolytic reduction and becomes 2 (R--S.sup.- .multidot.M.sup.+) by being bound to cations or protons (M.sup.+) in electrolytes, and its original linkage form R--S--S--R is restored at the time of electrolytic oxidation, emitting two electrons. In the secondary cell using said material, it is expected that an energy density of more than 150 Wh/kg, which is as good as that of other conventional secondary cells, will be achieved.
However, a report made by inventors of said United States Patent in J. Electrochem Soc., Vol. 136, No. 9, pp 2570-2575 (1989) has revealed that a speed of electron mobility in an electrode reaction in such secondary cells composed of disulfide compounds is extremely slow, which raises problems of making it difficult to take out a large electric current sufficiently adaptable for practical use at approximately a room temperature, thus restricting its use such that an ambient temperature should be 60.degree. C. or above.
Thereafter, in order to improve such a secondary cell composed of disulfide compounds for taking out a large electric current therefrom, as disclosed in a Japanese Patent Application Laid Open No. 5-74459, a material for an electrode employing organic compounds which have a disulfide group in combination with a conducting polymer, such as polyaniline, has been proposed.
In the technology using above-materials, however, though an increase of reaction rate has been achieved, no increase of energy density has been realized.
To overcome such defects in the prior art, some materials for an electrode composed of polysulfide compounds having serial sulfide linkages have been proposed by inventors of the present invention. However, it was found that a decrease in discharging capacity of the electrode using above-described materials has taken place due to a loss of sulfur from an oxidation/reduction through the repetition of charging and discharging of the cell, and therefore a proper means to prevent such a decrease have been sought.